Climate Projections Very Likely Underestimate Future Volcanic Forcing
and its Climatic Effects
Abstract
Standard climate projections represent future volcanic eruptions by a
constant forcing inferred from 1850-2014 volcanic forcing. Using the
latest ice-core and satellite records to design stochastic eruption
scenarios, we show that there is a 95% probability that explosive
eruptions could emit more sulfur dioxide (SO2) into the stratosphere
over 2015-2100 than current standard climate projections (i.e.,
ScenarioMIP). Our simulations using the UK Earth System Model with
interactive stratospheric aerosols show that for a median future
eruption scenario, the 2015-2100 average global-mean stratospheric
aerosol optical depth (SAOD) is double that used in ScenarioMIP, with
small-magnitude eruptions (< 3 Tg of SO2) contributing 50% to
SAOD perturbations. We show that volcanic effects on large-scale climate
indicators, including global surface temperature, sea level and sea ice
extent, are underestimated in ScenarioMIP because current climate
projections do not fully account for the recurrent frequency of volcanic
eruptions of different magnitudes.